Methane Mobility in Ag/H-ZSM-5 Zeolite in the Presence of Ethene: A View Based on PFG 1H MAS NMR Analysis of Methane Diffusivity

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• 作者：Sergei S. Arzumanov ; Daniil I. Kolokolov ; Dieter Freude ; Alexander G. Stepanov
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：August 13, 2015
• 年：2015
• 卷：119
• 期：32
• 页码：18481-18486
• 全文大小：314K
• ISSN：1932-7455

文摘

With regard to the influence of methane on the reactivity of ethene on Ag/H-ZSM-5 zeolite, the diffusivities of methane in the presence of ethene coadsorbed on Ag/H-ZSM-5 has been analyzed by PFG ¹H MAS NMR spectroscopy. It is established that the diffusion of methane in the absence of ethene occurs more slowly (activation energy E_a = 29 kJ mol^鈥?) than the diffusion of methane in the presence of coadsorbed ethene (E_a = 6鈥? kJ mol^鈥?). The higher value of E_a for the methane diffusion in the absence of ethene was related with some strong interaction of methane with Ag⁺ cations located in the zeolite channel system. Acceleration of diffusion and a decrease of its activation energy in the presence of ethene were assigned to the shielding effect of ethene adsorbed on Ag⁺ cations to form 蟺-complexes. An absence of direct interaction of methane with Ag⁺ cations was assumed to provide a significant decrease of activation energy and acceleration of methane diffusion. Two ensembles of methane molecules different by diffusivity have been assumed to exist in the zeolite in the presence of coadsorbed ethene. The presence of two ensembles of diffusing methane in the zeolite was rationalized in terms of the existence of two pathways of methane diffusion through the zeolite channel system. By one pathway, methane presumably diffuses over 蟺-complexes of ethene with Ag⁺ cations and the zeolite acid OH groups. The other pathway may include the methane diffusion in the zeolite channels exclusively over the zeolite OH groups.